1. Field of the Invention
This invention relates generally to vehicles having multiple engine drive systems and in particular to an arrangement for optimizing the performance of one engine in the absence of power input from the other.
2. Description of the Prior Art
In torque converter equipped vehicles, the torque converter is typically selected or sized to absorb maximum engine horsepower with its turbine or output stalled and at an engine speed or torque converter input speed corresponding to the peak torque engine speed. This insures that maximum engine horsepower will be available when the vehicle encounters operating conditions requiring maximum horsepower, as for example in surmounting a particularly steep grade. In some vehicles, such as heavy track laying type vehicles, high horsepower requirements and space limitations can combine to render a dual engine drive, as opposed to one very large engine, most desirable. In such a vehicle the power output of the dual engine arrangement is combined and delivered to a single torque converter sized to absorb the maximum dual engine power output. While this arrangement is satisfactory under dual engine operating conditions, interruption of power flow from one engine results in a capacity mismatch between the remaining engine and the torque converter and less than optimum utilization of what horsepower is available from the remaining engine. For example, with the converter turbine stalled or nearly stalled, the single engine would be lugged down below peak torque engine speed into an inefficient operating range so that continued operation on one engine, as might be necessary to return the vehicle to a service area for repair, would require that the engine operate in its least desirable speed range. A dual engine drive according to this invention represents an advance over other dual engine arrangements by virtue of its ability to make the most efficient use of the one active engine.
The primary feature, then, of this invention is that it provides a novel dual engine drive for a torque converter equipped vehicle, the novel drive permitting optimum operation of one engine in the absence of power input from the other. Another feature of this invention is that it provides a novel dual engine drive incorporating a gear transmission between the engines and the torque converter operative in the absence of power input from one engine to transform the power output of the remaining engine at constant horsepower to a lower speed and higher torque thereby to more efficiently match the torque converter. Still another feature of this invention resides in the provision in the novel dual engine drive of a two speed gear transmission between the engines and the torque converter having direct drive ratio for normal dual engine operation and a reduction ratio operative in the absence of power input from one engine to convert the power output of the other engine to lower speed and higher torque at constant horsepower thereby to more efficiently match the capacity of the torque converter while still maintaining optimum engine performance. A still further feature of this invention resides in the provision in the novel dual engine drive of a combining gear set for directing the power output of either or both engines to a single shaft, a planetary gear set having its ring gear driven by the single shaft, its planet carrier connected to the torque converter input shaft, and its sun gear selectively connectable to either the carrier, to provide direct drive for normal dual engine operation, or to a fixed portion of the transmission, to effect gear reduction in the absence of power input from one engine.